PCI-Express Riser/Extender Test

Published: July 7th, 2017 | Comments

Introduction

A few months ago I purchased a new Thermaltake P3 chassis. This case has the option to mount the graphics card vertically with PCIe extender. Unfortunately, that cable did not last very long, so I needed a replacement. After doing research my attention was quickly put towards ‘premium’ extenders, which are offered by few manufacturers, including Thermaltake and Lian-Li, whom I asked for a sample. It took many weeks to finally get all cables together, as few cheap cables from China were also ordered to give it a fair comparison.

I must say I have never spent so much time for one review. We are looking at a total of 4 days of nonstop testing. This is roughly 100 hours of testing, analyzing and writing. I will explain why it was necessary later in this review.

The idea behind this test is to tell you whether it’s really worth to pay x10 more for a premium cable. There is no denying that those cables are expensive, but chances are this cable will last for much longer, outlasting your graphics card.

This short review is also a debate about vertically mounted graphics cards. Motherboard manufacturers and PCI-SIG have not provided any alternative to graphics card installation other than the PCI-Express slot on your motherboard. All extenders are to comply with all PCI-Express standards, but there is no official standard for the cable itself.

But first, let me give you a very brief introduction to PCI-Express and types of extenders.


What is a PCIe extender/riser?

PCIe extenders became popular few years ago when the first bitcoin mining crazy has begun. At the time many different extenders were available, but only the popularity of mining has created a new market segment with 1x wide extenders. Those risers have a completely different purpose from the conventional riser. This review focuses on gaming risers, but we will test Bitcoin risers as well, to give you some idea what kind of performance difference are we looking at.

PCIe extender types

The words extender and riser are often used interchangeably. I prefer the word extender as it clearly points that the purpose of our cable is to increase the distance between the PCIe slot and the device itself.

Riser board

This is the most common riser used in rack servers, AIO desktops and systems where lack of space is a problem.

Unshielded ribbon riser:

This is the cheapest x16 riser you can find. Those cables have no EMI shielding, which can be a hit or miss for gamers.

Powered unshielded ribbon riser

Those extenders are recommended for Bitcoin miners, especially when more graphics cards are in use. In such situation motherboard may not deliver enough the power to each graphics cards, so Molex connector provides that power instead.

Shielded ribbon riser

This is a mid-range quality riser. It is not for miners, but gamers. These were popular few years ago, they are still bundled with some cases. Thermaltake and LianLi are now offering premium risers as a replacement, but you still need to pay for them.

 

Shielded ribbon riser with separated lanes

In this example, we are looking at Thermaltake premium cable. The lane separation has a big advantage over conventional riser, it gives you the flexibility. Those extenders should be the option for DIY gaming rigs on the wall.

 

USB ‘Bitcoin’ riser

This is by far the most popular riser type ever made. Recently motherboard manufacturers started offering 12x PCIe x1 motherboards designed specifically for those risers.

But wait, how is it even possible? PCIe x1 interface has 36 lanes, but only 14 are used for data transport and 6 of them are ground. This means That USB 3.0 cable with 9 wires is enough for PCIe 1x protocol.

Why do we need premium risers

The first and most important feature is the separation of PCIe lanes. As shown above, those cables are more flexible and give you much more freedom with graphics card installation. Some cables are separated by 5 or 6 lanes, others have power and data lanes separated.

Since premium cables are more likely to be used by gamers, those cables do not have any external power connectors. Additional power is only required for multi-GPU installation (4+) where it’s necessary to provide enough power for each graphics cards directly from the power supply.

Premium risers have higher quality PCIe slots. Before you buy any riser, it’s important to note which direction of the slot you need. Lian-Li cables are 90 degree slots, Thermaltake risers are straight with the slot directly on the other side of the cable.

Image courtesy of LiHeat Industry Co. Ltd.

There are few types of premium PCIe risers. It’s generally better to have power lanes and data lanes separated. The more cables risers have the more flexibility you get during installation, but also a higher risk of damage.

Comparison of Premium PCIe Extenders
Cable LiHeat Cable 3M Cable LianLI Cable Thermaltake Cable
Picture
Lane Shielding

PCI-Express: Difference between GT/s and Gbps

Before we move on, I think it’s a good opportunity to explain the difference between GT/s and Gbps. The GT/s also known as gigatranfers per second is not the same a gigabits per second (Gbps). PCI Express is a serial-based standard with the clock embedded in the data. The data is encoded in 8b/10b format, which means that every 8 bits are encoded into 10 bits. The overhead in encoding is used to align data stream at the receiver by allowing the clock to recover.

When we look at PCIe 2.0 specifications detailed in GT/s, we assume that this raw data transfer represents 80% of the encoded transfer speed of the data. Since PCIe 3.0 the encoding has been modified to 128/130b standard, it means that the overhead is smaller (1.54% vs 20%), thus it’s much more effective data transfer over raw GT/s from previous encoding standard.

PCI Express types, lanes and data rates

We can’t really talk about PCIe riser without knowing what PCIe is. These two charts are a very basic introduction to the topic. All risers in this review except the x1 one and USB riser, are advertised as X16 PCIe 3.0 riser. To some extent it’s true, I have not noticed any of those risers dropping to PCIe 2.0 specs. What this means is that each riser should theoretically offer the same bandwidth. In practice that is not always the case. Sometimes graphics cards change the PCIe specs to narrower standard (as reported by GPU-Z). This means that some lanes may be affected by interference and GPU data transport is reduced to x8. To comply with x16 standard we need all 142 pins connected at both ends.

PCI-Express Widths
Standard Total No. Pins No. of Variable Pins Total Variable
×1 2×18 = 36 2×7 = 14 25 mm 7.65 mm
×4 2×32 = 64 2×21 = 42 39 mm 21.65 mm
×8 2×49 = 98 2×38 = 76 56 mm 38.65 mm
×16 2×82 = 164 2×71 = 142 89 mm 71.65 mm

The PCIe 3.0 standard is quite old. There are no PCIe 4.0 graphics cards at this time, but PCI-SIG already announced preliminary PCIe 5.0 specs, which are to be approved by all involved parties. I think it’s still a long time before we start seeing 5.0 devices.

PCI-Express Revisions
Transfer rate x1 x4 x8 x16
PCIe 1.0
 
2.5 GT/s
 
0.25 GB/s
 
1 GB/s
 
2 GB/s
 
4 GB/s
PCIe 2.0
 
5 GT/s
 
0.50 GB/s
 
2 GB/s
 
4 GB/s
 
8 GB/s
PCIe 3.0
 
8 GT/s
 
0.99 GB/s
 
3.9 GB/s
 
7.9 GB/s
 
15.8 GB/s
PCIe 4.0
 
16 GT/s
 
1.97 GB/s
 
7.9 GB/s
 
15.8 GB/s
 
31.5 GB/s



by WhyCry